Screw cutting die



Dec 6, 1932- J. MILLERCHIP ETAL 1,890,124

SCREW CUTTING DIE Filed May 1l, 1932 Patented Dec. 6, 1932 Lasern UNT STTS FFE'CE DHH E/IILLERCHIP, OF LANE COVE, AND THOMAS MORRISON LAMBERT, OF ARTARMON,

NEVI SOUTH WALES, AUSTRALA SCREW CUTTING DE Application filed May 11, 1932, Serial No. 610,664, and in Australia May 6, 1931.

This invention relates to screw cutting dies oi the type in which a 'set comprises separate integers which are fitted in hand voperated stocks or in machine die holders or heads.

in the usual construction otdies the land is planar (in other `Words the teeth are straight) and is disposed at an acute angle to cutting face so that in operation it is n.. AL'ential to the Work. To re-sharpen such dies the cutting face is ground, and this operation, by reducing the Width of the land or length et' the teeth, also materially reduces the radial depth of the die with the result that an over-size thread is cut. It is known to provide in stocks or heads means for ad- ;,iustment to compensate for this reduction of radial length, but there is a limit to this adiusl'ment and repeated grinding so reduces the radial length that the die becomes useless.

Furthermore, in the manufacture of a set of dies With straight teeth the blanks have to be very carefully set and elaborate means emploj-,f'efl to cut the teeth so that those of each die will register l roperly when the set is tted in a stock or machine head.

An object'ot the present invention is to provide a die Which will be more serviceable and etlicient than dies With straight teeth and also less liable to damage as regards the cutting points ci the teeth.

second object is to provide a die which nay be reshav )cned in the usual Way, by lrinding the cui ing or leading face, Without educing the radial length to the same extent hat such operation would produce in a die 7ith straight teeth, thereby prolonging the effective liie of the die.

Another object of the invention is to provide die (or a set of dies) which is more simply manufactured than those With straight teeth, the formation of the teeth being effected through the instrumentality of ordinary screw-cutting tap, and Which will still furnish the necessary clearance or "3 relief rear-Ware lv of the cutting edge While having teeth oconstant depth throughout their length (except as regards the usual tapered starting teeth).

VEhese objects are achieved by the provision of eccentric relief or clearance of the cutting teeth in relation to the Work. In other Words the land of the die instead of being planar, is concavely curved, the curve being struck from a centre which is non-coincident With or eccentric to the centre of the Work to be operated upon, or with or to the centre of the stock or machine head in which the die 1s mounted, as hereinafter more fully explained.

One effect ot t iis curved or eccentric clearance is that While the cutting angle of the points of the teeth may be as required forl the particular material to be operated upon, the graduated clearance of the teeth rearwardly ot the pointsV is less those of straight teeth which are tangential to the Work, and in consequence the portions of the teeth rearwardly of the points, more closely engage the grooves or threads cut by the points, thus serving to resist any twisting of the dies onthe Work (with consequent possible damage to the points) and also producing a cleaner and.

smoother thread. p

Moreover', the radial depth of the die does not diminish from the leading :tace to the trailing or rear tace to the same extent as in a die With straight'teeth, and consequently the grinding of the leading face does not reduce the radial depth to the same extent as does equivalent grinding of adie having straight teeth. In other Words the clearance, though existent, is considerably less than that in a die having straight teeth, and this effect is produced Without any sacrificing of the depth of the teeth, which is uniform throughy out their length, except of course as regards further object of the present invention is the provision ot dies any of which in a set, on account of the fastening means, may be removed Without disturbing the others. In the accompanying drawing: Fig. l is a perspective view of which the finished dies are litted,

a stock in '50c stock having a radial slot on one side'by which Fig. 2 is a cross-sectional elevation thereof, and passing through the stock andengaging Fig.V 3 is a cross-sectional elevation .of the a threaded bore in the die. j stock and dies. Y Signed `at Sydney, New South Wales, Fig. 4 Vis a diagram (drawn t0 a, largerV Australia this eighth day 0f ApIl,A. 13.71932. scale) clearly showing the eccentric clearance JOHN MILLERGHIP- or relief of the die in relation to the work. Y THOMAS MORRISON LAMBERT A complete screw cutting tool including a Y set of dies, and adapted for hand operation, is shown in Figs. 1, 2 and 3.` It consists in a K y j Y ystock comprising a short cylinder 12 equipped Y 75 with radial handles 121and formed at itsV ends with internal annular ianges 122 between which lit the dies 18 their arcuate bases fitting snugly against thewall ofthe cylin- Y y j *Y der. Passing radially through the cylinder Y 33 wall are holding screws 13 which engage the y' 1 threaded holes 5 (hereinbefore described) in the dies and serve toY hold Vthe latter in position. i Y Y To permit'dametric adjustment of the cylv Y rv 35 inder it is split as at 19, and two radial lugs l 16are engaged by a pinchingscrew 16l the adjustment of which'effects the required con-V Y traction or expansion of the stock in known Y Y f mannenv To produce more uniform flexing of Y 1 9C the stock, three half slots 1'?, spaced at 90 intervals, are provided. n VIt will vbe observed that the bases or outer.V vedges of the dies are curved to the same'radius Y c c c as the inner periphery of the stock, andthat Y g 96 the lands or toothed surfaces are eccentric to the stock. n This eccentricity is clearly Y shown in Fig. 2 andparticularly -in Fig. 4 35 in whichV the work is represented by circle Y v mi, 14, and the leading face of the die indicated Y n at 64; 1 Y

It will also be noted that any single die may be removed without disturbing the 1 others. n' Y For centering the workv there is provided K Y lo a guide consisting of a collar 20 having spider i arms* 21 secured by screws 2 2 to the stock. A removable ferrule 23 of'appropriate diameter to the work in hand is fitted in the collar 20. p Y What we claim and kdesire to secure byLetters Patent is: A i -V A A screwV cutting tool, comprising a circular f Y it is split, and an adjusting screw passing through and connecting the split portions, said stock being further provided on the inner side with notches, one opposite the slot and j 55 the others intermediate said notch and said y .f

slotand dividing the stock into sections, and

a set' of dies each havingia convex arcuate base and a concavely curved land or toothed surface eccentric to the base7 each die being f eo arranged in the stockwith its convex base p Y Y Y Y j 125 bearing against one section thereof and in Vcontact with said section throughout its en# tire length and concentricwith the inner cylindrical surface of the stock-and a radial G5 screw releasably securing each die in the stock Y A' 130 

